The A’s were dealt a couple of very tough losses in the first two games against the Giants. On Friday, Ryan Cook, who entered with an 0.57 ERA, gave up four runs in the ninth to take a blown save and a loss. On Saturday, the A’s rallied for four runs in the ninth, only to come up just short and lose 9-8.

Today, the A’s finally got it done, all thanks to Derek Norris’ first major league homer.

Norris delivered a three-run shot in the bottom of the ninth off Santiago Casilla, giving the A’s a 4-2 victory. It was just the second blown save in 22 opportunities for Casilla.

Norris was called up last week to share time with the struggling Kurt Suzuki behind the plate for Oakland. Today’s start was his third as a big leaguer, but he already has more RBI (four) than Suzuki does in the last month (three).

The A’s comeback ruined Matt Cain‘s streak of victories in eight straight starts. No one else has won more than six consecutive starts this season, though R.A. Dickey will go for No. 7 tonight. Cain didn’t figure in the decision, obviously, but this marked the first time since May 1 than the Giants had lost one of his starts.

Sweet! After a badly blown call by the first base ump who missed Seth Smith’s on-the-line double and called it foul, denying the A’s the tie and go ahead runs, the walk-off was mightily welcome.

The other big story was rookie AJ Griffin holding the Gigantes to two runs, both courtesy of Posey’s first inning blast. Griffin had excellent command and the bright glare, which I had expected Thursday with Kershaw in town, held the hitters back for just a fraction and depressed scoring.

Overall an excellent series in which both teams scored 16 runs, but the Giants won two of three and take the Bay Bridge 2012 season series 4 games to 2.